The present invention relates to ceramic implant materials which can be implanted in a living body, such as artificial roots of teeth or artificial bones.
Ceramic materials are characterized by the fact that rejection of them by a living body is only slight and they are not corroded easily and, therefore, the use of them as implant materials such as artificial roots of teeth or artificial bones is expected. Thus, the use of various ceramic materials as implant materials has been studied and a variety of clinical examples wherein they are used have been reported since about 15 years ago.
Single-crystal or polycrystalline alumina, for example, is a material against which the rejection by a living body is slight, and investigations have been made on the use of it as the implant material. However, since the tissue does not easily adapt itself to said alumina and since the strength and hardness of the alumina are excessively high, the tissue in contact with the aluminous ceramic is often inflamed or abraded.
Polycrystalline silicon nitrides and zirconia which are attracting attention recently also have the defects that the tissue does not adapt easily itself to them and they do not adhere to the tissue and, therefore, no interference layer can be formed between them. Consequently, when a strong impact is applied to them, the tissue is inflamed.
On the other hand, though calcium phosphates such as hydroxyapatite or tricalcium phosphate comprising components very close to those constituting natural bones have excellent adaptability to the tissue, their strength and toughness to a sudden impact or stress applied when they are used as the artificial roots of teeth or artificial bones are yet insufficient. They are thus unsuitable for use as the implant materials.
Under these circumstances, investigations were made on composite materials comprising a core made of an aluminous ceramic and a surface layer made of hydroxyapatite or tricalcium phosphate to which the tissue easily adapts itself. However, these composite materials require considerable labor and steps in the preparation thereof and they are yet unsatisfactory for use as the implant ceramics, since the adhesion between the calcium phosphate constituting the surface layer and the aluminous ceramic constituting the core is insufficient.